This invention relates to a method of fabricating a stator assembly for a multiple-pole dynamoelectric machine (e.g., an induction motor) and to a stator assembly made in accordance with the method of this invention.
In certain electric motor applications, such as in ceiling fans, the motor is designed to run at a relatively low or slow speed. For example, a ceiling fan motor may be operated at 350 R.P.M. These motors may have 18 poles, as compared to more conventional 2, 4, 6, or 8 pole motors.
Conventionally, the windings for these multiple-pole motors comprise concentrically wound coil sets each having a plurality of separate, individual coils electrically interconnected with one another, one coil for each pole of the motor. Thus, for an 18 pole motor, there would be required 18 separate coils of magnet wire for the main winding of the motor and 18 separate coils of magnet wire for the auxiliary winding of the motor. Each of these individual coils typically had a large number of turns of magnet wire therein. For example, each main winding coil of an 18 pole ceiling fan motor may have 185 turns or more of No. 27-No. 30 wire. Because of the large number of turns and the large number of poles in the motor, these 18 pole ceiling fan motors are difficult and expensive to manufacture. Additionally, conventional coil winding and inserting techniques utilized to manufacture these prior ceiling fan motors were labor intensive and were thus expensive.
Typically, prior art concentrically wound coil set motors, such as illustrated in FIG. 4 of the drawings in the instant specification, have a plurality of coils (e.g., 18) of magnet wire electrically connected to one another and inserted in the slots of the core of the stator assembly so as to form, for example, the main and auxiliary windings of the motor. Because of the high number of turns of wire in each of the coils, the end turns of the coils (i.e., the portions projecting out beyond the end faces of the stator core) are, of necessity, bulky and cannot readily be formed into a tight radius. During operation of the motor, current must flow through the end turns of the windings, but the end turns do not serve to generate any substantial portion of the rotating magnetic field of the motor. Since the resistance losses of the motor are dependent primarily upon the length of the magnet wire contained in the windings, it is desirable to make the end turns of the windings as small as possible. Additionally, a considerable amount of copper magnet wire is consumed by the end turns which makes these prior art motors costly.
Still further, because of the large end turns normally associated with such prior art concentrically wound coil, multiple pole motors, it was necessary to lace or tie the end turns of the auxiliary and main windings of the motor together with textile lacing material or the like thereby to hold the windings in place. This requirement of lacing the end turns was, of course, costly as it did require a substantial amount of labor and materials.
In an effort to reduce the size of the end turns, and yet to maintain the same operating characteristics of the motor, a prior art concentrically wound coil motor was developed in which the number of coils of the motor was doubled, but in which the number of turns per coil was halved. Further, the coils in this motor, as shown in FIG. 5, were split so that each pole for the main and auxiliary winding was constituted by a coil with the legs of adjacent coils sharing a common slot. While this did somewhat reduce the size of the end turns and did result in wire savings, it became a problem to wind such a large number of coils, to transfer the coils from the winding apparatus to the inserting apparatus, and to insert them into the slots of the core. This fabrication process required a considerable amount of labor, was time consuming, and was therefore expensive.
Still further, it is known to skein wind the windings of an electric motor. In a skein wound motor, the windings are formed by first winding a large coil or skein of magnet wire in the shape of a circle. Then, the skein is formed to be a petalled, serpentine shape having a plurality of inner and outer apices (e.g., 9 inner apices and 9 outer apices) with straight coil sections or legs extending between the apices. Such skein wound motor windings may be made on the apparatus and in accordance with the method disclosed in the co-assigned U.S. Pat. No. 4,357,968 issued to Vernon E. Kieffer. However, because these prior art skein windings were relatively thick and had a multiplicity of turns of magnet wire therein, they also had relatively large end turns.